Flotation apparatus



United States Patent 3,437,203 FLOTATION APPARATUS Koichi Nakamura, 2270 Kichijoji, Musashinoshi, Tokyo, Japan Continuation-impart of application Ser. No. 345,277, Feb. 17, 1964. This application July 5, 1967, Ser. No. 651,187 Claims priority, application Japan, Feb. 20, 1963, 38/7,.386; May 7, 1963, 38/22,656 Int. Cl. B03d 1/20 {1.8. Cl. 209-169 6 Claims ABSTRACT OF THE DISCLOSURE A froth flotation machine including an aerator assembly having a set of guides surrounding its impeller, each of said guides being set at such an angle with respect to the radius of the aerator assembly which passes through its inner end as to cause logarithmic spiral flow of pulp or the like issuing from the impeller to be laminar, the outer ends of said guides being advanced in the direction of rotation of the impeller beyond the inner ends of said guides. A circular flange is located above the outer ends of the impeller blades. The concentrate froth discharge lip is located in the cell wall in the annular zone of V-shaped cross-section which lies above the plane of the circular flange and below a cone tangent to the lower extremities of the impeller blades and to the outer edge of the flange. The guides may be turned from their laminar flow inducing positions to compensate for the presence of supply pipes or the like in the annular zone. The guides may also be thus turned to compensate for non-circularity of the cell in which the aerator is located.

C ross-reference to related application This is a continuation-in-part of my copending United States Patent application Ser. No. 345,277, filed Feb. 17, 1964, now abandoned, the filing date of which is claimed for all subject matter herein and disclosed therein.

Background of the invention This invention relates to flotation apparatus for use in froth flotation. More particularly, this invention relates to froth flotation machines of the type known as agitationfroth machines which have one or more aerators in each of which there is a rotating impeller surrounded by a plurality of blades or vanes. The function of these blades or vanes in the prior art is to act as bafl le means and produce bafliing current or turbulence in the air-pulp mixture issuing from the impeller, by contrast with the guides of the present invention which reduce the turbulence produced by the pulp-feed or the horizontal cross-sectional shape of the cell to unimportant magnitudes.

In addition, the devices of the prior art are commonly provided with foraminous screens to aid in quieting the turbulence within the cell produced by the baffle means. These screens found in prior art devices also act as bubble size selectors. According to the present invention these screens are no longer necessary, since, as may be experimentally demonstrated, the size of the bubbles in devices embodying the present invention is a function of flotation conditions, such as pH, type of reagent, type of frother, and the like.

While these turbulence producing blades, vanes, buflies, and the bubble size selecting screens of the prior art may be said to contribute to the production of a rich and active froth in the upper reaches of the flotation cell, it is also evident that they lower the over-all flotation efliciency in the sense that the impeller driving power required to pass aerated pulp through them is considerably greater than that which would be required to drive the impeller in their absence.

Summary of the invention According to the present invention, however, these turbulence producing baflie blades or vanes may be replaced with a set of guides which are oriented substantially laminally, i.e., parallel to the mean direction of the logarithmic spiral flow issuing from the impeller, in the manner of the guides in a turbine centrifugal pump, wherein each guide blade is set at such an angle with respect to a radius of the pump, its outer edge leading its inner edge in the direction of pump rotation, that laminar flow results. When the turbulence inducing baflie blades or vanes of the prior art are thus replaced with guides which are constructed and arranged to produce laminar flow in an annular zone, and the froth discharge lip located in said annular zone as taught hereinafter, there results a device of improved over-all efliciency.

According to another aspect of the present invention, when the aerator according to the invention is employed in cells of non-circular horizontal cross-section, or in cells in which supply pipes pass through said annular zone of V-shaped cross-section within the body of aerated pulp, thereby tending to produce turbulence in the flow of pulp, the guides may be turned from their optimum position of laminal flow production to empirically determined positions in which the over-all eificiency of the device is optimized.

It is therefore an object of the present invention to provide froth flotation apparatus from which certain baffles or turbulence. producing and power consuming ele ments of the prior art devices are absent.

It is a further object of the present invention to provide flotation apparatus characterized by simplicity of construction and operation.

Yet another object of the invention is to provide such flotation apparatus having improved over-all efficiency.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

Brief description of the drawing For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

FIG. 1 is a sectional view of one section of a flotation apparatus according to the present invention taken along line 11 of FIG. 2;

FIG. 2 is a sectional view of the device of FIG. 1 taken along line 2-2 of FIG. 1.

Description of the preferred embodiments Referring now to FIGS. 1 and 2, it may be seen that a device embodying the present invention includes a number of parts found generally in agitation-froth flotation machines of the prior art. For instance, the device of FIGS. 1 and 2 comprises a tank or cell 1, which may be but one of a co-operating series of such tanks or cells in the well-known manner. Further, the horizontal cross-section of tank or cell 1 may take the shape of a square 1", an octagon 1, or other non-circular shape, all as wellknown in the art (see FIG. 2), and compensation for such deviation from the preferred horizontal circular cross-section 1 may be made in accordance with the teachings of the present invention as set out hereinbelow.

A vertical shaft 12 is journalled for rotation about the vertical axis of tank 1 by means of bearings of which only the lower one is shown. An impeller generally designated 20 is affixed to the lower end of shaft 12 for rotation therewith. Impeller 20 comprises a plurality of blades 3 which are aflixed to a disk-like member 14' and thereby maintained equally spaced about and equidistant from shaft 12 with the plane of each blade including the vertical axis of tank 1, all in the well-known manner. The upper end of shaft 12 is provided with a pulley 22 by means of which impeller 20 may be rotated by prime mover means not shown. Surrounding shaft 12 is a main air tube 2 by means of which air is conducted from the region above the top of tank 1 to the neighborhood of impeller 20 in the well-known manner. An inner air tube 25 may be disposed within tube 2 in the usual manner, both of said tubes being supported by conventional support means not shown. A circular flange 4 projects outwardly from the lower end of main air tube 2 and extends beyond the outer extremities of blades 3. Froth outlet 8 passes through cell wall 6 within the angle defined hereinafter.

A supply pipe 11 extends from an opening 10 in the wall of tank 1 to an opening 9 in the wall of tube 2. Supply pipe 11 is adapted to be used for supplying pulp or the like to air tube 2 in the well-known manner. As shown at the top of FIG. 2, an additional supply pipe 11' may also be provided, which may be used if it is desired to supply intermediate pulp to the air tube as well-known in the art.

When the device of FIGS. 1 and 2 is used in a series arrangement of the type known in the art, it may be provided with means 28, 29 communicating with adjacent tanks wherein pulp inlet means 10 and tailing discharge means 27 are located in the well-known manner, or the aerator unit comprising the impeller and the air tube may be mounted along with other similar units in a single tank, as is also well-known in the art.

A set of guides is disposed between flange 4 and the bottom of tank 1. As best seen in FIG. 2, guides 5 are substantially equally spaced around the periphery of the impeller 20 at a sufficient distance therefrom so that the impeller is free to rotate within the cage formed by flange 4, guides 5, and the central part of the bottom of tank 1. Each one of the guides 5 makes substantially the same angle with a line 32 drawn tangent to the periphery of flange 4 at the point where the guide intersects flange 4. Thus, the right-most guide 5 shown in FIG. 2 can be seen in that figure to make an angle p with a line 32 drawn tangent to the periphery of flange 4 at the point 4 at which the top edge of said right-most guide 5 meets the periphery of flange 4. In this setting position the outer end of each guide is always advanced in the direction of rotation of the impeller beyond its inner end, and thus said angle p is always less than ninety degrees. The angle p between the plane of any guide 5 and its corresponding line 32 may hereinafter be called the amended guide angle.

According to the present invention the common angle which all of the guides in a given embodiment make with their corresponding tangent lines is selected so that the guides produce laminar flow in the spiral efllux from impeller 20, or so that the over-all flotation efliciency of the device is maximized when the tank is of non-circular cross-section, when there is a supply pipe located in such a way as to interfere with the flow of aerated pulp from between guides 5 to the froth discharge opening, or when both of these conditions exist. Thus, it may be seen that it is a principal feature of the present invention to set the guides outside the impeller at such as angle as to maximize laminar or non-turbulent flow to the greatest possible extent consistent with maximum flotation efiiciency. This is contrary to the prior art which teaches the employment of blades or vanes outside the impeller which are so oriented as to produce maximum turbulence, or a controlled degree thereof.

It is further necessary, according to the present invention, when making use of the impeller and guide combination of the present invention, to locate the froth discharge opening within an annular zone which is generally symmetrical about the axis of shaft 12. The vertical crosssection of this annular zone is generally V-shaped, being shown as angle 74'7 in FIG. 1 and hereinafter designated E. More particularly, this annular efllux zone of V-shaped cross-section may be defined as the space lying above the plane of the lower face of flange 4, below a cone which is tangent to the lower extremities 3' of impeller blades 3 and the outer edge 4' of flange 4, and within the outer wall 7' of tank 1 or an upward extension thereof.

As may be seen in FIG. 1, a device of the present invention will desirably be free of such obstructions in the annular efliux zone as the bubble size selecting screens or perforated hoods commonly found in devices of the prior art. Thus, in accordance with the teachings of the present invention, the freest possible flow of aerated pulp from the output zone of the aerator to the froth discharge opening is promoted.

In prior art froth flotation devices of the type referred to herein the flow of the aerated pulp from the impeller to the froth discharge means has generally been broken up by intentionally introduced baflle or impact producing means such as radially disposed turbulence producing blades or vanes located immediately outside the impeller. Thus, since it has been considered preferable in the prior art to prevent generally smooth upward and outward spiraling circulation of the aerated pulp issuing from the impeller, the prior art has not recognized the adverse effect upon flotation efliciency resulting from the presence of one or more pulp supply pipes extending from the wall of the tank to the main air tube within the body of eflluent aerated pulp.

The present invention, however, recognizes the problem of lowered flotation efliciency resulting from the presence of such a supply pipe in the eflfluent aerated pulp. in particular, the present invention recognizes the problem of the presence of such a supply pipe, or pipes, within the above-mentioned annular efflux zone of V-shaped crosssection. Thus, according to the present invention, the increase in resistance to the generally spiral circulation of aerated pulp when such a supply pipe is employed may be compensated by deviating the guides from their angle of laminal flow by empirically determined amounts such that the flotation efiiciency of the device is maximized. Impairment of the smooth outward and upward flow of aerated pulp from the impeller resulting from the tank having non-circular horizontal cross-section may similarly be compensated by deviation of the guides from their angle of laminal flow by an empirically determined amount. Thus when it is desired to employ aerator units according to the invention in existing flotation cells which are of non-circular horizontal cross-section or have submerged supply pipes, the present invention teaches that the guides may be deviated from their position of laminal flow which they would occupy in an optimum flotation cell sufiiciently to raise the empirically determined flotation efliciency to levels approaching that attained when such an optimum flotation cell configuration is employed. The same expedient may, of course, be adopted in newly constructed flotation cells when non-optimum cell configuration or supply pipe location is found to be more economical.

It can also be noted, when the smooth outwardly and upwardly spiraling pulp flow pattern of the invention is employed, that the circulation of pulp on the upper surface of the pulp body or concentrate froth takes the form of an outwardly directed spiral flow path advancing from the side of the air tube to the circumference of the tank. Thus, the employment of the relatively smooth flow pattern according to the invention tends to promote efficient circulation of the pulp throughout the pulp body. When empirically determining the optimum deviation of the guides from their laminal flow positions in order to compensate for non-circular cross-section of the tank or the presence of a supply pipe in the pulp body, these determinations may be conveniently and efliciently carried out by the use of the following formula. It will be noted that in so doing the extent of angular deviation necessary for tank shape compensation may be determined independently, and the extent of deviation necessary to compensate for the effect of a single supply pipe may then be determined independently, whereafter the effect of these factors may be combined according to the formula.

The formula is:

where is the optimum setting angle of each guide for a cell which has no obstacles in the annular etflux zone, 0 being always less than 90; p is the amended setting of each individual guide (p is always S 0); n is the number of supply pipes; I is the experimentally determined deviation necessary to compensate for the presence of a single supply pipe; and is the deviation necessary to compensate for the shape of the tank used.

By empirical compensation carried out in accordance with this formula the flotation efliciency of a cell employing the aeration unit of the present invention may be raised to substantially that of a circular, non-obstructed cell employing the aeration unit of the invention.

Also, it is preferable to provide a frusto-conical transition plate 13 between air tube 2 and flange 4 (FIG. 1), so that the aerated ore pulp stirred by impeller blades 3 can be prevented from backflowing to air tube 2 in the well known manner.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. Froth flotation apparatus, comprising:

container means,

supply means,

froth outlet means,

tailing discharge means located in said container means,

impeller means disposed within said container means,

motive means for rotating said impeller means,

flange means extending outwardly from said supply means adjacent said impeller means and overlying and projecting beyond said impeller means, and

a plurality of equidistantly spaced guide vane means mounted in a substantially circular array surrounding said impeller means and located in the path of the efliux issuing therefrom,

each of said guide vane means being so angularly positioned as to produce laminar flow in said efflux when said container means is free from supply pipes and is of circular horizontal crosssection, the outer edge of each of said guide vane means being further advanced in the direction of rotation of said impeller means than its inner edge, and

said froth outlet means being located in the wall of said container means above the plane in which said flange means lies and below a cone tangent to the periphery of said flange means and to the lowest points of the outer edges of the blades of said impeller means,

whereby said efliux is caused to spiral smoothly upwardly and outwardly toward the lip of said container means and the circulation of pulp on the surface of the pulp body in said container means takes the form of an outwardly directed spiral advancing toward the lip of said container means in laminar flow.

2. Froth flotation apparatus as claimed in claim 1 in which the path followed by said efliux from said guide vane means to said froth outlet means is substantially unobstructed.

3. Froth flotation apparatus as claimed in claim 1 in which the path followed by said efliux from said guide vane means to said froth outlet means is obstructed only by said supply means.

4. Froth flotation apparatus, comprising:

container means,

supply 'means,

froth outlet means,

tailing discharge means located in said container means,

impeller means disposed within said container means,

motive means for rotating said impeller means,

flange means extending outwardly from said supply means adjacent said impeller means and overlying and projecting beyond said impeller means, and

a plurality of equidistantly spaced guide vane means mounted in a substantially circular array surrounding said impeller means and located in the path of the efliux issuing therefrom,

each of said guide vane means being so angularly positioned as to make an angle 5 with an optimum angular position which results in laminar flow in said efllux when said container means is free from supply pipes and is of circular horizontal cross-section, the outer edge of each of said guide vanes being further advanced in the direction of rotation of said impeller means than its inner edge, whereby the flotation efficiency of the apparatus is maximized, and said froth outlet means being located in the wall of said container means above the plane in which said flange means lies and below a cone tangent to the periphery of said flange means and to the lowest points of the outer edges of the blades of said impeller means, said angle 6 being determinable from the formula where n is the number of supply pipes in said efllux path, I' is the experimentally determined angular deviation necessary to compensate for the presence of a single supply pipe in said efflux path, and is the angular deviation experimentally found to be necessary to compensate for the shape of the horizontal cross-section of said container means when said container means is non-circular in horizontal cross-section.

7 5. Froth flotation apparatus as claimed in claim 4 in which said container means is of non-circular horizontal cross-section.

6. Froth flotation apparatus as claimed in claim 4 in which said supply means passes through said efliux above said plane and below said cone.

References Cited UNITED STATES PATENTS 1,796,278 3/1931 Bakewell 261-87 1,985,153 12/1934 Daman 261-93 2,104,349 1/1938 MaCCamy 209-169 FOREIGN PATENTS 5/1937 Great Britain. 3/1939 Italy.

TIM R. MILES, Primary Examiner.

US. Cl. X.R. 

